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Warping of Terrace Pavers at the U.S. Capitol Building.

pdf icon Warping of Terrace Pavers at the U.S. Capitol Building. (1329 K)
Ferraris, C. F.; Stutzman, P. E.; Clifton, J. R.

NISTIR 5847; 25 p. May 1996.

Available from:

National Technical Information Service
Order number: PB96-193651


building technology; aggregates; alkali-silica reaction; cements; concretes; construction materials; expansion; pavers; warping


The terraces of the U.S. Capitol are covered with cement-based pavers designed to emulate the granite pavers used elsewhere on the Capitol grounds. The pavers were warped after three years of service. These pavers are composed of two layers; an upper, decorative white-cement-based mortar with crushed micaceous quartz aggregate supported by a base of conventional concrete. Field inspection and laboratory testing indicates the warping is probably due to the high cement content, environmental exposure conditions, and possibly differences in hydraulic length changes of two layers comprising the pavers. A cement content of nearly twice that found in typical concretes, leads to higher levels of moisture-driven swelling and shrinkage. This coupled with the different exposure environments of the two materials, i.e., higher relative humidity under the paver and faster drying on the top of the paver, and the differential hydraulic length changes of the two materials used in the pavers leads to warping. Alkali-silica reactivity (ASR) tests indicate that the base layer aggregate is marginally reactive and the upper layer aggregate is non-reactive. While some reaction products were observed in the base layer, expansion due to alkali-silica reaction was not thought to be a significant cause of the warping of the pavers.